Nate Silver: “One word of warning: factors like early voting, crossover voting and the relatively large amount of demographic diversity within Michigan will make it tricky to call the state based on exit poll results and the first few precincts that report. For instance, if early and absentee results are reported before those cast on Election Day, as is common in some states, Mr. Romney could initially emerge with a lead that proved ephemeral. I generally take the view that the news networks are too quick to call a race — shouldn’t have we learned something from Florida in 2000 or Iowa this year? — but there is reason to be especially cautious here.”

Voters head to the polls today in Michigan’s surprisingly competitive Republican presidential primary.
The primary is open; any registered voter can vote.

First Read: “Tonight will largely decide if Romney limps to the nomination or if all hell breaks loose inside the GOP. There’s no overstating the consequences of a Romney loss tonight: There won’t just be handwringing by the establishment, but there will be financial and staffing consequences, too.”

Meanwhile, a top Republican strategist unaligned with a presidential campaign tells The Note that no matter what happens in Michigan today,
“Romney will have to battle weakness concerns rest of campaign.”

All polls will be closed at 9 pm ET.

GOP strategist Matthew Dowd to George Stephanopoulos:

“If Rick Santorum wins tonight it’s the equivalent of a 9.0 on a Richter scale. I mean it is going to shake Washington, it’s going to shake Republican establishment it’s just going to shake things to their very core. And I think what you’re going to see are the conversations that have been going on behind quiet doors saying we need another candidate in this race.”

A super PAC supporting Newt Gingrich has received another “substantial” contribution from billionaire casino magnate Sheldon Adelson and will launch television ads in seven states this week, the Washington Post reports.

The ads will begin today in Georgia, Oklahoma, Ohio and Tennessee, with more to come Wednesday in Mississippi, Alabama and Kansas.

David Brooks: “All across the nation, there are mainstream Republicans lamenting how the party has grown more and more insular, more and more rigid. This year, they have an excellent chance to defeat President Obama, yet the wingers have trashed the party’s reputation by swinging from one embarrassing and unelectable option to the next: Bachmann, Trump, Cain, Perry, Gingrich, Santorum. But where have these party leaders been over the past five years, when all the forces that distort the G.O.P. were metastasizing?”

“Sen. Santorum did something today which I think is deceptive and a dirty trick.”

— Mitt Romney, quoted by CNN, on his rival using robocalls to seek the support of crossover Democrats.

National Republican leaders “are voicing increasing dismay over the course of the party’s presidential primary, which has fallen into such a negative grind that they warn it could cost them the White House,” Politico reports.

“At the core of their concern is the atmosphere of daily vituperation between the top candidates. Mitt Romney, Rick Santorum and Newt Gingrich are now engaged in a seemingly constant knife fight, interrupted by only the sparest of positive, policy-oriented debate.”

Notes former Pennsylvania Gov. Ed Rendell (D): “In terms of sustained negativity, there’s nothing like it in history.”

A new Washington Post-ABC News poll finds just 38% of “very conservative” Americans now express favorable views of Mitt Romney. That’s his lowest mark of the campaign among staunch conservatives and down 16 percentage points over the past two weeks.

A final Public Policy Polling survey in Michigan conducted over the last two nights shows Rick Santorum just edging Mitt Romney in the GOP presidential primary, 38% to 37%, with Ron Paul at 14% and Newt Gingrich at 9%.

However, the results for the last night show a decided shift in momentum toward Santorum, leading Romney by five points, 39% to 34%, with Paul at 15% and Gingrich at 10%.

Rick Santorum’s presidential campaign “is actively seeking the support of Democrats in Tuesday’s Michigan primary, running a robocall that sounds oddly like one that would be run by an organized labor group,” the Washington Post reports.

TPM: “Michigan’s primary rules allow Dems to vote in the state’s GOP primaries. The liberal site DailyKos and other progressive partners have been trying to drum up enthusiasm for ‘Operation Hilarity’ — an effort to get Democrats to vote in the GOP primary and tilt the vote against Mitt Romney. The Santorum campaign evidently decided they’d take votes from any legitimate source.”

Harry Enten notes that three Michigan polls from last Thursday found Mitt Romney leading Rick Santorum by an average of 5.7 points. However, Romney’s average lead in polls taken over the weekend is down to just 1 point.

Meanwhile, a Public Policy Polling survey in the field tonight is already picking up on “encouraging things for Santorum.” The full poll results will be out late tonight.

If true, it could be a late night tomorrow waiting for primary results to come in.

A new WPRI 12 poll in Rhode Island’s 1st congressional district finds challenger Brendan Doherty (R) crushing Rep. David Cicilline (D-RI), 49% to 34%, with 16% still undecided.

Jonathan Chait: “The modern GOP — the party of Nixon, Reagan, and both Bushes — is staring down its own demographic extinction. Right-wing warnings of impending tyranny express, in hyperbolic form, well-grounded dread: that conservative America will soon come to be dominated, in a semi-permanent fashion, by an ascendant Democratic coalition hostile to its outlook and interests. And this impending doom has colored the party’s frantic, fearful response to the Obama presidency.”

Mitt Romney recalled childhood memories of a landmark moment in Detroit history, noting he was “probably 4 or something like that” the day of the Golden Jubilee, to celebrate the 50th anniversary of the American automobile, the Toronto Star reports.

Said Romney: “My dad had a job being the grandmaster. They painted Woodward Ave. with gold paint.”

Unfortunately, the event took place June 1, 1946 — fully nine months before Romney was born.

After a rough election cycle for Democratic chairmen of House committees in 2010, The Hill provides a rundown of the Republican chairmen facing difficult reelection battles, including a few primary challenges.

Nate Silver‘s latest forecast shows Romney still has the advantage in the Michigan GOP primary tomorrow “but it is more tenuous than the one we released overnight. The model gives him a 64 percent chance of winning the state, down from 77 percent in the previous forecast.”

The reason? Five new polls are out today with three showing Romney in the lead and two putting Santorum ahead.

Steve Kornacki: “The familiar Romney campaign formula — wait for conservative rival to emerge, beat back conservative rival with attack ads and strong debate performance, prevail in do-or-die primary test, wait for next conservative rival to emerge — may be in the process of repeating itself in Michigan. But the final polling in advance of tomorrow’s primary contains some serious hints of trouble for Romney.”

Wisconsin Gov. Scott Walker (R) will not challenge any signatures by Monday’s deadline in an attempt to stop a recall election against him, the Milwaukee Journal-Sentinel reports.

“That leaves only a review by state elections officials standing
between the Republican governor and only the third recall election for a
governor is U.S. history.”

Joshua Spivak has an excellent look at what to expect next.